FR2651995A1 - Ring for acetabular implant - Google Patents

Abstract

The ring for an acetabular implant is distinguished by the fact that it comprises arrangements (1a) (1b) which are capable of cooperating, on the one hand, with the ischiopubic foramen of the iliac bone and, on the other hand, with the upper part of the acetabulum at the level of the external iliac fossa, in order to ensure its fixation in the said acetabulum, in combination with at least one member (3) screwed into the latter.

Description

 The invention relates to the technical sector of hip prostheses in particular.

Many types of cotyloidal implants are known to replace the cotyloid cavity of the pelvic bone. In essence, these implants comprise a metal ring generally of hemispherical shape whose bore receives a plastic core shaped to receive the femoral head of a prosthetic element. However, it is advisable to distinguish - the rings fixed in the acetabulum by means of a suitable cement, of those which are not,
The invention relates more particularly to the rings of the type intended to be fixed in the acetabulum without cement. In this regard, there are several known solutions or methods generally three in number.

 According to a first method, the ring is impacted by force in the bone acetabulum, which is milled to a determined diameter. This method is not satisfactory and little used, because after a while, a large game appears between the ring and the acetabulum. Indeed, the bone tissue fits imperceptibly to the diameter of the ring.

 According to another solution, the periphery of the ring has arrangements constituting a thread, for screwing said ring into the acetabulum. As before, a game can occur. In addition, this thread has an equal pressure on the entire circumference of the acetabulum, which is not satisfactory on a biomechanical level, since in reality, the acetabulum works only in its upper zone. So there are additional constraints.

 Finally, according to another solution, the ring is fixed in the acetabulum by means of at least one screw which is oriented very substantially according to the resultant forces exerted on the iliac bone, at the acetabulum to reduce the shear forces. . This method of fixation is satisfactory in the case of a slightly damaged acetabulum, where the hemispherical cavity is always well formed. Of course, in reality, this is not the case. It is necessary in most cases to reconstitute the sphere and perform a transplant.

 Under these conditions, again, the fixation obtained is not safe and satisfactory.

 The purpose of the invention is to remedy these disadvantages.

 To solve the problem of ensuring a secure and effective fastening of the ring, without cement, by eliminating any stress phenomenon with perfect primary and secondary stability, the ring according to the invention is remarkable in that it comprises arrangements adapted to cooperate, on the one hand, with the ischio-pubic hole of the iliac bone and, on the other hand, with the upper part of the acetabulum at the level of the external iliac fossa, to ensure its fixation in said acetabulum in combination with at least one member screwed into the latter.

 The problem posed is advantageously solved in that the arrangements consist of a curved and profiled lower leg intended to cooperate with the ischiopubic hole by creating a hooking effect and by an upper tab shaped to bear with a part of the external iliac fossa. .

 To improve the attachment, the upper lug has two side lugs arranged to receive a fastener of the screw type.

 To solve the problem of minimizing the shearing forces, the fastener or members are engaged in holes formed in the thickness of the body of the ring and arranged so that the said member or bodies are oriented very substantially in the axis of the resultant forces exerted on the acetabulum; the holes receiving the fixing screw or screws and the upper and lower tabs are arranged in the same axial alignment.

 As a result, the clamping effect exerted on the screw in the acetabulum has the effect of putting in tension the lower leg which is hooked with the edge of the ischiopubic hole.

 According to another characteristic, the upper leg and the lower leg are diametrically opposed.

 In one embodiment, the upper lug is formed in radial overflow from the periphery of the body of the ring while the lower lug is formed in radial overflow of a peripheral recess of said body.

 The ring has a symmetrical shape, which allows to impact it indifferently, in a right or left acetabulum.

 For. In order to solve the problem of taking into account important bone grafts, the upper leg is capable of receiving an extension member capable of being fixed in an established bone graft for restructuring the acetabulum.

The invention is described below, in more detail, with the aid of the accompanying drawings, in which
- Figure 1 is a perspective view of an embodiment of the ring according to the invention; there is illustrated before mounting an embodiment of the core to be positioned in the ring.

 - Figure 2 is a bottom view of the ring.

 - Figure 3 is a plan view showing the positioning and fixation of the ring in the acetabulum of the iliac bone.

 FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 3.

 - Figure 5 is a partial view showing a portion of the ring equipped with an extension member.

 In a known manner, the metal ring generally designated by (1) has a generally hemispherical shape, the bore of which receives a core (2> made of plastic material, especially polyethylene, and this ring may be subjected to a treatment. in the form of a plasma spray to which calcium hydroxalapalite is added.

 According to the invention the ring (1) has arrangements (la) (Ib) shaped to cooperate on the one hand with the ischio-pubic hole (03) of the iliac bone (O) and on the other hand with the upper part of the acetabulum (01) at the level of the external iliac fossa coq2). These arrangements, (la) (Ib) are intended to ensure the attachment of the ring (i) in the acetabulum CO1? in combination with at least one member (3) passing through said ring to be screwed into said cup.

 As shown in Figure 2, in a preferred embodiment, the ring (1) has a curved lower leg and profiled (la> creating a hooking effect when engaged in the ischio-pubic hole CO3>. In contrast, the ring has an upper lug (1b) shaped to bear with a portion of the external iliac fossa.The lower (1a) and upper (lob) lugs are arranged in the same axial alignment being diametrically opposed. .

The upper lug (1b) is formed in radial overflow from the periphery of the body of the ring while the lower lug (1b) is formed in radial overflow of a peripheral recess (Ic) of said body Cfigure 1>. the upper leg (lb) is folded downwards by forming an angle relative to the horizontal (CoL) to fit in bearing on the anatomical profile of the iliac fossa (Figure 4>. Advantageously, the upper leg (lob) ) has two side lugs C1bl) Clb2) arranged to receive a fastener of the screw type (4>
The screw (3) is engaged in a hole Cld) formed in the thickness of the body of the ring (1> being arranged so that said screw is oriented very substantially in the axis of the resultant forces exerted on the acetabulum This hole (id) and the legs Cla> and (lob) are arranged in the same axial alignment.

 It therefore appears that a tightening effect exerted on the screw (3> for fixing the ring (1) has the effect of putting in tension the lower tab (1a) in the hooking position and support on the edge of the ischio-pubic hole This tab (la) is thus subjected to a reaction force CF) (Figure 4). Of course, without departing from the scope of the invention, it is not possible to form in the thickness of the body of the ring several holes for receiving a corresponding number of screws taking into account, as indicated above, their position. relative to the resultant forces exerted on the acetabulum.

 Advantageously, the attachment of the ring can be completed by means of two screws (4) engaged in the ears of the upper lug (lb) (Figures 3 and 4).

 According to another feature, the upper lug (1b) can receive an extension member (5) adapted to be fixed in an established bone graft to restructure the acetabulum and the corresponding portion of the iliac fossa. This extension member is fixed in combination with the screws (4) of the ears of the upper lug (lb). As shown in the embodiment illustrated in Figure 5 the end of this extension member also has two side lugs arranged to receive the fasteners.

 Given the asymmetrical shape of the two iliac bones the extension member (5) has a curved profile oriented either on the left side or on the right side.

The advantages come out well in the description, we emphasize in particular
- Safe and effective fixing obtained by the combination of the two legs (la) and (nib) including the lower leg with the screw (3). Note that in the case of a slightly damaged acetabulum, it is not necessary to use the fixing screws (4) of the upper leg, the screw (3) and the lower hooking tab being largely sufficient.

 - The safety of the fixation obtained, even in the case of a very large bone graft, given the extension member can be attached to the upper leg of the ring.

 - the fully symmetrical shape of the ring.

 Of course, the outer periphery of the body of the ring is subjected to any known and appropriate surface treatment capable of ensuring good secondary stability.

Claims (10)

R E V E N D I C A T IO N S  -1 cotyloldien implant ring characterized in that it comprises arrangements (la) (lb) adapted to cooperate, on the one hand, with the ischio-pubic hole of the pelvic bone and, on the other hand, with the upper part of the acetabulum at the level of the external iliac fossa, to ensure its attachment in said acetabulum in combination with at least one member C3) screwed into the latter. -2- ring according to claim 1, characterized in that the arrangements are constituted by a lower leg (la) curved and profiled intended to cooperate with the ischiopubian hole by creating a hooking effect and by an upper lug (lob) shaped for take support with part of the external iliac fossa. -3- Ring according to claim 2, characterized in that the upper lug (lb) has two side lugs arranged to receive a fastener type screw (4). -4- Ring according to claim 1, characterized in that the or the fasteners (3) are engaged in one or holes <10) formed in the thickness of the body of the ring and arranged so that the or said members are oriented very substantially in the axis of the resultant forces exerted on the acetabulum. -5- Ring according to claims 2 and 4, characterized in that the holes receiving the fixing screw or screws and the upper and lower tabs are arranged in the same axial alignment. Ring according to claim 2, characterized in that the upper lug (1b) and the lower lug (1a) are diametrically opposed. -7- Ring according to claim 2, characterized in that the upper lug (lob) is formed in radial overflow of the periphery of the body of the ring while the lower lug (la) is formed in radial overflow of a recess peripheral (lc> of said body.  -8- Ring according to any one of claims 1 to 6, characterized in that it is symmetrical. -9- Ring according to any one of claims 2 and 3 characterized in that the upper lug (lb) is capable of receiving an extension member (5) adapted to be fixed in an established bone graft to restructure the acetabulum. -10- Ring according to claim 8 characterized in that the extension member has a curved profile corresponding to the right iliac bone or the left iliac bone.